1. Field of the Invention
The present invention relates to a projection apparatus and, more particularly, to a projection apparatus suitable for, e.g., a liquid crystal projector for projecting image information displayed on a light modulation element such as a monochrome liquid crystal, color liquid crystal (color liquid crystal panel), or the like for forming an image onto a screen in an enlarged scale.
2. Related Background Art
Conventionally, various liquid crystal projectors for projecting image information displayed on a liquid crystal panel, which is a light modulation element, onto a screen have been proposed.
FIG. 18 is a schematic view showing principal part of the optical system of a color liquid crystal projector using a reflection liquid crystal, which is proposed by Japanese Laid-Open Patent Application No. 6-265842. This optical system is called a Schlieren optical system.
Referring to FIG. 18, light emitted by a light source 1 is converted into nearly collimated light by a reflector 2 (parabolic mirror), is reflected by a mirror 3, and is then focused to form a light source image near a reflection mirror 5 placed at the stop position of a projection optical system 13. The light beam reflected by the reflection mirror 5 travels toward a plano-convex lens 7, and is converted into collimated light by the plano-convex lens 7. The collimated light is color separated into three, R, G, and B light beams by a cross dichroic prism 8 to respectively illuminate reflection liquid crystal panels 9, 10, and 11 for forming images of the respective colors (wavelength ranges).
The R, G, and B light beams modulated by the reflection liquid crystal panels 9, 10, and 11 are color-synthesized into full-color image light by the cross dichroic prism 8 again. The full-color image light is focused by the plano-convex lens 7, passes through a stop 12, and is then projected onto a screen 15 via the projection optical system 13.
In each liquid crystal panel, for example, a polymer dispersed liquid crystal or polymer network liquid crystal is sealed. When white level is displayed, the liquid crystal becomes transparent to specularly reflect a light beam; when black level is displayed, the liquid crystal scatters and reflects (diffusely reflects) a light beam. The light beams which are reflected by the liquid crystal panels and color-synthesized by the cross dichroic prism 8 are focused at or in the vicinity of the position of the stop 12 of the projection optical system 13. Most of the light beam reflected by each liquid crystal panel pass through the aperture of the stop 12, and display white level on the screen 15 via the projection optical system 13. However, little of the light scattered by the liquid crystal panel pass through the aperture of the stop 12, thus displaying black level on the screen 15.
In this way, image information is displayed using scattering of the liquid crystal, and is projected onto the screen via the projection optical system.
The above-mentioned stop 12 will be explained below with reference to FIG. 19. FIG. 19 shows the relationship between an aperture 12a of the stop 12 placed at the pupil position of the projection optical system (projection lens) 13, and a light source image Sxe2x80x2. A pupil 16 of the projection lens 13 has a semi-circular shape since its half portion is occupied by the reflection mirror 5. The light source image Sxe2x80x2 represents a mode in which the liquid crystal panel reflects an incoming light beam to display white. In case of the other mode in which the liquid crystal panel scatters an incoming light beam to display black, the light source image Sxe2x80x2 becomes sufficiently larger than the aperture 12a, and only a part of the entire light beam pass through the aperture 12a. If the size of the aperture 12a is increased, the amount of light that reaches the screen 15 increases, and a bright projected image can be obtained. However, since the luminance of black level similarly rises, the contrast lowers. If the size of the aperture 12a is decreased, the contrast can be improved, but the projected image becomes dark. Thus, the brightness and contrast of the projected image normally have a trade-off relationship.
However, in the color liquid crystal projector shown in FIG. 18, even when an aperture 12a smaller than the light source image Sxe2x80x2 is used to give priority to contrast over the brightness of the projected image, the contrast cannot be improved.
This problem will be explained using FIG. 19. When the light source image Sxe2x80x2 is classified into portions inside and outside the aperture 12a, only the former portion contributes to the brightness of the projected image when white is displayed on the liquid crystal panel. However, when black is displayed on the liquid crystal panel, since a light beam incident on the liquid crystal panel is scattered, both light beams focused inside and outside the aperture 12a are partially diffused and pass through the aperture 12a. Hence, the contrast lowers due to the presence of the latter light beam.
It is an object of the present invention to provide a projection apparatus suitable for a high-resolution liquid crystal projector such as a computer monitor, which can project image information with high contrast.
According to one aspect of the present invention, there is provided a projection apparatus which guides a light beam emitted by a light source to at least one light modulation element for forming an image, and projects the light beam coming from the light modulation element onto a screen or the like, by a projection lens wherein a stop is located at a position conjugate with an aperture of a stop of the projection lens to intercept a part of the light beam emitted by the light source.
According to another aspect of the present invention, there is provided a projection apparatus which guides a light beam emitted by a light source to at least one light modulation element for forming an image, and projects the light beam coming from the light modulation element onto a screen or the like, by a projection lens comprising: first optical means for forming an image of the light source as a first light source image; and second optical means for re-imaging the light beam coming from the light modulation element illuminated with light emanating from the first light source image at a position in the vicinity of an aperture of a stop of the projection lens as a second light source image, wherein a peripheral portion of the first light source image is intercepted by stop means located at a position conjugate with the stop of the projection lens.
According to still another aspect of the present invention, there is provided a projection apparatus, which has color-separation means for separating a white light beam emitted by a light source into a plurality of light beams corresponding to different wavelength ranges, optical means for guiding the plurality of light beams to a plurality of light modulation elements for forming images corresponding to the respective wavelength ranges, synthesizing means for synthesizing the light beams coming from the plurality of light modulation elements, and a projection lens for projecting the light beam synthesized by the synthesizing means onto a screen or the like, comprising: first optical means for forming images of the light source as first light source images; and second optical means for imaging light beams coming from the plurality of light modulation elements illuminated with light beams emanating from the first light source images to re-form second light source images of the light source at or in the vicinity of a stop position of the projection lens via the synthesizing means, wherein peripheral portions of the first light source images are intercepted by stop means located at a position conjugate with the stop position.
According to still another aspect of the present invention, there is provided a projection apparatus comprising: color-separation means for separating a white light beam emitted by a light source into a plurality of color light beams corresponding to different wavelength ranges; first lens means for imaging the color light beams coming from the color-separation means to form first light source images of the light source; deflection means, located in the vicinity of the imaging position of the first lens means, for deflecting and guiding the light beams to a plurality of light modulation elements for forming images corresponding to the respective wavelength ranges; second lens means for re-imaging the color light beams from the plurality of light modulation elements to form second light source images of the light source; synthesizing means for deflecting at least one of the light beams coming from the plurality of light modulation elements, and synthesizing the deflected light beam with the remaining light beams; and a projection lens for projecting the light beams modulated by the plurality of light modulation elements onto a screen or the like, wherein the second light source images are formed at or in the vicinity of a stop position of the projection lens, the synthesizing means is placed near the stop position of the projection lens to split an aperture thereof, and peripheral portions of the first light source images for the respective colors are intercepted by stops provided for the respective at a position conjugate with the stop position in color light beams.
According to another aspect of the present invention, there is still provided a projection apparatus, which has a light source, focusing means for focusing a light beam emitted by the light source to form a light source image, light guiding means, having first and second end faces, for receiving the light beam from the first end face and outputting the light beam from the second end face, the light guiding means being constructed by reflection surfaces which connect the first and second end faces, and reflecting and guiding at least a part of the light beam received from the first end face to the second end face, optical means for guiding the light beam coming from the second end face to an image modulation element, a projection lens for projecting an image on the image modulation element onto a screen, and optical means for focusing and guiding the light beam modulated by the image modulation element on a position of an aperture of a stop of the projection lens, wherein the first end face is located in the vicinity of a focusing position of the light source image, the apparatus further has first optical means for forming an image of the first end face to generate a first light source image, second optical means for imaging the first light source image as a second light source image in the vicinity of the stop position of the projection lens, and third optical means for setting the second end face at a position conjugate with the image modulation element, and a peripheral portion of the first light source image is intercepted by stop means located at a position conjugate with the stop of the projection lens, thereby substantially reducing the size of the second light source image.
According to still another aspect of the present invention, there is provided a projection apparatus which guides a light beam coming from an illumination system to at least one image modulation element, and projects the light beam coming from the image modulation element onto a screen via a projection lens, wherein a peripheral portion of the light beam is intercepted by stop means inserted in the illumination system at a position conjugate with an aperture of a stop of the projection lens, thereby limiting the light beam that passes through the aperture of the stop of the projection lens.
According to still another aspect of the present invention, there is provided a projection apparatus which guides a light beam coming from an illumination system to at least one image modulation element, and projects the light beam coming from the image modulation element onto a screen via a projection lens, wherein an image of a light source in the illumination system is formed on a predetermined plane as a first light source image by first optical means, the light beam emanating from the first light source image is guided to the image modulation element, the light beam coming from the image modulation element is formed as a second light source image at or in the vicinity of a position of an aperture of a stop of the projection lens by second optical means, and a peripheral portion of the first light source image is intercepted by stop means inserted in the illumination system at a position conjugate with the aperture of the stop of the projection lens, thereby reducing the size of the second light source image.
According to still another aspect of the present invention, there is provided a projection apparatus which color-separates a white light beam coming from an illumination system into a plurality of color light beams by color-separation means, guides the plurality of color-separated light beams to image modulation elements provided for the respective color light beams, synthesizes the light beams coming from the image modulation elements by synthesizing means, and projects the light beam synthesized by the synthesizing means via a projection lens, wherein an image of a light source in the illumination system is formed on a predetermined plane by first optical means as a first light source image, the light beam emanating from the first light source image is guided to the image modulation elements, light beams coming from the image modulation elements are formed by second optical means as a second light source image at or in the vicinity of a position of an aperture of a stop of the projection lens, and a peripheral portion of the first light source image is intercepted by stop means inserted in the illumination system at a position conjugate with the aperture of the stop of the projection lens, thereby reducing the size of the second light source image.
According to still another aspect of the present invention, there is provided a projection apparatus which color-separates a white light beam coming from a light source of an illumination system into a plurality of color light beams by color-separation means, forms first light source images of the respective color light beams on a predetermined plane by first optical means, guides light beams emanating from the first light source images to image modulation elements provided for respective color light beams using deflection means, images the light beams coming from the image modulation elements on a predetermined plane as second light source images of the respective color light beams by second optical means, and projects the light beams emanating from the second light images onto a screen via a projection lens, wherein synthesizing means is located at or in the vicinity of a stop position of the projection lens to split an aperture thereof, at least one of the light beams from the plurality of image modulation elements are deflected toward the projection lens, and stop means for the respective color light beams are inserted in the illumination system at a position conjugate with the aperture of the stop of the projection lens to intercept peripheral portions of the first light source images, thereby reducing the size of the second light source image.
According to still another aspect of the present invention, there is provided a projection apparatus which guides a light beam coming from an illumination system to at least one image modulation element, and projects the light beam coming from the image modulation element onto a screen or the like via a projection lens, wherein the illumination system has a hollow or solid rod integrator with an inner reflecting surface, an image of a light source in the illumination system is formed at an entrance end face of the rod integrator by optical means, an image of the entrance end face of the rod integrator is formed on a predetermined plane by the first optical means as a first light source image, a light emanating from the first light source image is guided to the image modulation element, the light beam coming from the image modulation element is imaged by second optical means as a second light source image at or in the vicinity of a position of an aperture of a stop of the projection lens, an exit end face of the rod integrator is conjugate with the image modulation element, and a peripheral portion of the first light source image is intercepted by stop means inserted in the illumination system at a position conjugate with the aperture of the stop of the projection lens, thereby reducing the size of the second light source image.
According to one aspect of the present invention, the light modulation element comprises a transmission light modulation element using a polymer dispersed liquid crystal.
According to one aspect of the present invention, the light modulation element comprises a reflection light modulation element using a polymer dispersed liquid crystal.
According to one aspect of the present invention, the light modulation element comprises a transmission light modulation element using a polymer network liquid crystal.
According to one aspect of the present invention, the light modulation element comprises a reflection light modulation element using a polymer network liquid crystal.
According to one aspect of the present invention, the color-separation means for separating the white light beam coming from the light source into the plurality of light beams corresponding to the different wavelength ranges comprises a diffraction grating.
According to one aspect of the present invention, the color-separation means for separating the white light beam coming from the light source into the plurality of light beams corresponding to the different wavelength ranges comprises a plurality of dichroic mirrors placed to tilt each other.
According to one aspect of the present invention, the synthesizing means comprises a cross dichroic prism.
According to one aspect of the present invention, the synthesizing means comprises a plurality of mirror means for reflecting the light beam.
According to one aspect of the present invention, the deflection means comprises a plurality of mirror means for reflecting the light beam.
According to one aspect of the present invention, an optical system which sets the stop means at a position conjugate with the aperture of the stop of the projection lens includes at least one aspherical lens.
According to one aspect of the present invention, an optical system which sets the stop means at a position conjugate with the aperture of the stop of the projection lens shares at least a portion of the second optical means.
According to one aspect of the present invention, an optical system which sets the stop means at a position conjugate with the aperture of the stop of the projection lens shares at least a portion of the second lens means.
According to one aspect of the present invention, an optical system which sets the stop means at a position conjugate with the aperture of the stop of the projection lens shares at least portions of the second and third optical means.
According to one aspect of the present invention, the light beam that enters the aperture of the stop is set to have a size substantially the same as an aperture of the stop means.
According to one aspect of the present invention, the second light source image is set to have a size substantially the same as the aperture of the stop.
According to one aspect of the present invention, the aperture of the stop of the projection lens comprises a variable stop, and another variable stop, an aperture size of which changes in association with the variable stop is located at a position conjugate with the aperture of the stop of the projection lens.
According to one aspect of the present invention, the light guiding means, having the first and second end faces, for receiving the light beam from the first end face and outputting the light beam from the second end face comprises a glass rod having a hexahedron shape, and totally reflects at least some light components of the light beam that enters the glass rod from the first end face to guide the light components to the second end face.
According to one aspect of the present invention, the deflection means and stop means are located at positions where the deflection means and stop means do not interfere with each other.
According to one aspect of the present invention, the stop means is located in the vicinity of imaging position of the first light source image, and separated a predetermined distance from the imaging position of the first light source image.